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Since ASP.Net first came, it came up with a very powerful feature of in-memory object cache (System.Web.Caching.Cache) to store commonly used expensive data on server side. Almost every ASP.Net application/site uses this feature now. But it suffered from few shortcomings like-

It is available in ASP.Net only leaving WinForms or WPF clients puzzled.

It is not extensible to accommodate other demands to store cache objects in disk or Sql Server. However, MS after realizing these shortcomings, Caching Application Block library was included in its Enterprise Library.

.Net developers have to look for their own mechanisms to create logical in-memory partitions called regions to group or organize cache objects in memory.

The System.Runtime.Caching namespace contains two core set of classes:

Concrete implementation of System.Runtime.Caching.MemoryCache class to support in-memory object cache. MemoryCache is closely modeled after old System.Web.Caching.Cache of ASP.Net. However, one does not have to rely upon System.Web assembly to use MemoryCache (We will see it through an example shortly).

Now let’s move to try out an example to leverage MemoryCache features. First of all we will create a class library type project. Add a class MyCache and assembly reference of System.Runtime.caching.dll.

MyCache Code sample:

using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Runtime.Caching;

Now we can debug above code and see other interesting things. You will see the usage of MemoryCache methods and its techniques to cache objects are similar to what we have been doing in ASP.Net cache so far. Also, we see how the same MyCache library is usable in both web and windows applications.

MemoryCache points worth mentioning:

MemoryCache.Default returns the single and same instance of in-memory ObjectCache through a static read-only property.

public static MemoryCache Default { get; }

CacheEntryRemovedCallback signature is different than what we have seen in prior versions of ASP.Net. Refer to example. In the current callback method, one can see the following details when cache item is expired after 10 seconds.

CacheItemPriority enum in .Net 4.0 is cleaner than what we have seen in prior versions of ASP.Net. Now, it is only Default and NotRemovable.

In prior version of ASP.Net, CacheDependency was used to monitor changes in any underlying objects like files, Sql database tables, rows, columns, etc. Now .Net 4.0 provides ChangeMonitor class which is ASP.Net neutral and has wider scope of monitoring dependent objects to expire cache items. However, CacheDependency is still there in ASP.Net 4.0. We should use other implementation of ChangeMonitor like HostFileChangeMontor in the above example.

The default implementation of MemoryCache does not give us flexibility to add regions along with keys. In order to use regions, you should extend MemoryCache.

Strategy design pattern falls under the category of Behavioral Design Pattern. In this pattern, we capture abstraction in an Interface or Abstract class called Strategy Base, and we bury implementation details of algorithms in concrete classes called Concrete Strategy. Client code can then call such different implementation methods based upon some strategy or condition during run time. Client is not tied statically or bound to call fixed methods, rather it can change its strategy dynamically. This is because client never calls any methods directly by instantiating concrete classes. Client sets its strategy via some other class called Context.

We see each of the concrete strategy class implementing algorithm to calculate upon numbers in its own way- one doing addition, while other doing subtraction. But their over all capability to do arithmetic operations upon numbers is abstracted inside Calculate(int, int) method in StrategyBase class.

See the Context class above. It has a property Strategy to get-set of type StrategyBase type. Alternatively, Context class can get-set instance of StrategyBase by a constructor or some method as well like SetStrategy(StrategyBase objSB).

But why do we require this Context class? Because clients agree to call any ConcreteStrategy method not directly. Clients will only hint out for such concrete strategy. What does this mean? This means a lot- Strategy pattern lets you change the guts of an object.

Template method design pattern falls under the category of Behavioral Design Pattern. In this pattern, a template method defines a skeleton of an algorithm in terms of abstract operations. The template method can contain one or more steps. But these steps will have to be in abstract form only. That said, we cannot change the order of steps, and most importantly we cannot override the template method itself. Only the steps given in the skeleton of algorithm of template method need to be overridden in concrete classes.

We see the concrete classes are overriding the abstract operations defined by the template method in its algorithm. This way template method pattern provides an abstract view of algorithm.

So in practical scenario, this pattern fits only when different types of object instances are required to invoke methods or operations that differ sharply in implementation but the algorithm remaining same. Also, sometimes when are refactoring multiple classes, we can find template method pattern coming into picture.

Important point to note here is: the way we are calling TemplateMethod() of ConcreteClassA from base class AbstractAlgorithmSkeleton reminds us of “The Hollywood Principle”- “Do not call us, we will call for you”. That is, child class method is being called from base class. This way of method call is also known as Inversion of Control.

Decorator design pattern falls under the category of Structural Design Pattern. Structural design pattern emphasizes upon the overall structure of classes and objects in the system either by doing class inheritance or by composing objects into larger structures using object composition. Decorator pattern comes handy when we want to add additional responsibilities to the object during run time.

Additional responsibilities can be added statically by class inheritance also. But this will create another problem when we want to add such responsibilities to objects of many classes. We may have to create many child classes to support additional new functions.

So instead of creating many child classes of already existing concrete classes, we create a new Decorator, and a new Concrete Decorator class that will add new methods and properties to the existing class object during run time. This way we are not modifying the existing concrete or legacy classes. Responsibilities to objects can be added during runtime because base class of the object and Decorator class share the same base type. And Concrete Decorator class extends the new Decorator.

This design pattern does not come initially during system design. It generally comes during maintenance phase or later in the development phase.

Now let’s see the example of decorator design pattern. We even use mobile phone to send text and multimedia messages. Once the message is sent, the Outbox becomes empty. But sometimes we want to save the sent content message. To do this, we need to select the option of “Send and Save”, and any message sent this way will be saved inside “Sent” folders. Here, even if the user may not always want to save the sent messages, it is for sure that he may definitely want to send messages. Keeping this use case in mind, let’s look into such a class design.

Fig: Base class for SMS and MMS Concrete Classes

Fig: Overall class structure after the introduction of Decorator

From the above diagram, we see two main concrete classes that are involved in sending messages- MobileMMS sends image as message content while MobileSMS send text. Both of the classes are doing well with SendMessage() method. SendMessage() is an abstract method in BaseMessage root class. Decorator, often called DecoratorBase, can be seen inheriting from the same base type of these two MobileMMS and MobileSMS classes, i.e.; inheriting from BaseMessage class. For a Decorator class this is important.

Then, we see MessageProcessor class (often called ConcreteDecorator) which is a concrete implementation of Decorator.

Note: BaseMessage, MobileMMS and MobileSMS are the original classes. Only due to SendAndSave option, a new responsibility SaveMessage() is now required to be added into the objects of MobileMMS and MobileSMS. This is how we see DecoratorBase and ConcreteDecorator need to be added later on.

Now see the SendSMS and SendMMS methods: how the constructor methods of MessageProcessor are accepting object instances. This is called object composition, and important for Concrete Decorator. This way MessageProcessor will be able to direct the call to the actual method of the class. See the SendMessage() method code above in MessageProcessor.

.Net Assemblies can contain various types of resources like images, icons, files, etc. Such resources are mostly static, i.e.; do not keep changing during run time or application wise. Also, such resources are not executable items. So while deploying such assemblies, we need to make sure those resources are intact with the packaged assemblies. Else, assemblies may blow up while executing the resource dependent methods. So as part of deployment strategy, we should embed such resources into the assembly itself.

Today we will see one such example of embedding Xml file into assembly.

Add one Class Library type project into the solution.

Add one Xml file as well. Fill Xml file with few data that the class library may use to query.

Right click on the Xml file, and select Properties –> BuildAction. Out of several BuildAction options, select EmbeddedResource.

There you may see other properties as well like Copy to Output Directory. It has options like this:

If you select Do Not Copy, output of building the class library inside \bin\ folder will not have separate *.dll than embedded Xml file.

If you select Copy Always, output of building the class library inside \bin\ folder will always have *.dll and an embedded Xml file.

However, I prefer the first option. By this we make sure our distributable assembly is only one *.dll. This way the embedded resource Xml file cannot be modified, and our assembly can safely execute methods that depend upon this Xml file. I like to suggest one more tips here- rename this Xml file extension to *.config. Renaming Xml file extension to *.config makes file not browse able by Browser in web applications.

Here I have shown steps of embedding resource file into .Net assembly. This assembly can be either Class Library or Web application. We cannot embed resource file into web site type project as Web site does not produce assembly like Web application.

Now, let’s see how we can access embedded Xml file from assembly during runtime.

There are two methods shown above- one returning XmlDocument object and other returning IO.Stream. Either of the return type can be used to construct XmlDocument object now at caller end of these methods.

Now let’s verify the assembly if it has any embedded resource or not. We can do this using either Reflector or Ildasm tool.

Reflector View:

Ildasm View:

See resource name is qualified with assembly namespace name prefixed to it- MathLibrary.XMLFile.config.

Coding less and debugging more has always been part of programming. Debugging of code is always accompanied by locating appropriate break-points and inspecting program execution. But locating break points again and again whenever a solution is opened for debugging consumes time. When we feel the program execution is happening as expected, then we either delete break-points or disable them. Overall, programmers spend few minutes for break-points activities.

Visual Studio 2010 comes with new feature of exporting and importing break-points in an xml file. So when we are done with break-points, we can export and save at a physical location. Then, delete the break-points (Ctrl + Shift + F9). Whenever we require break-points again in code, we can import the settings file that we saved last time. This xml file contains all the required settings of break-points in the code like line number, file name, etc.

Snapshots shown below are self-explanatory for .Net programmers.

Open break-point window (Ctrl + Alt + B).

Fig 1: Exporting break-points

Fig 2: Importing break-points

After importing break-point xml file, the break-points are again set at lines and files where break-points were set originally.

ViewStateMode – ViewState for Individual ControlsASP.Net 4.0 allows view state in a page to be more controllable from page to its child controls level. That is, view state of a control can be enabled or disabled irrespective of its parent control’s view state. Even if view state of a page is disabled, controls of the page can have their own view state individually enabled or disabled or even inherited from the page’s view state mode property. This property if utilized properly can certainly boost performance of a page.

For example, we can individually enable or disable user control’s view state in a page.

By default, ViewStateMode is enabled for a page object, while controls have inherit mode.

Page.MetaKeywords and Page.MetaDescription – SEO Optimization FeatureASP.Net 4.0 has come up with these two properties that will help developers add meta tags for keywords and description in the aspx pages in easier fashion. Web Search Engines really need these two meta tags for search indexing of any pages. These two properties can be used in a page in various ways. Inside <head> tag or in the code behind or even at <%@Page%> directive level.

However, setting meta keywords or description in code behind will be more useful when we have to add keywords and descriptions dynamically from source like database.

MetaKeyWords is used to store few useful keywords that will briefly highlight important information of a page by tags. From SEO perspective, meta keywords should contain keywords separated by spaces.

MetaDescription is used to add page description in short that will help Search Engines to quickly describe about the page links in search pages.

Prior to ASP.Net 4.0, we have to add meta tags using HtmlMeta control (public class HtmlMeta : HtmlControl) adding into page header as:

In classic ASP or ASP.Net earlier than 4.0, we used to redirect to new pages or links by setting Response.StatusCode to 301 before calling Response.AddHeader method. Now ASP.Net 4.0 has provided Response.RedirectPermanent method to redirect to new pages or links with StatusCode of 301 implicitly set. Search Engines use this 301 code to understand permanent redirection from old pages links.

Web.config now looks cleaner as most of the settings are controlled from machine.config file as ASP.Net 4.0 is all set to benefit from IIS 7 and IIS 7.5 features. When IIS is set to use .Net 4.0 and Integrated Pipeline mode, <compilation> element holds .Net version attribute. And the traditional <httpHandlers> and <httpModules> section is now shifted out of <system.web> and added inside new section <system.webserver>. All the custom handlers are added inside <handlers>, and all the modules inside <modules> section.